This invention relates to compositions containing L-selenomethionine and the other selenoamino acids in a topical carrier for prevention of ultraviolet (hereinafter "UV") radiation-induced skin damage, and to a method of preventing such skin damage using selenoamino acids. The invention further relates to a method for preferentially increasing the selenium concentration in selected parts of the skin such that ultraviolet radiation-induced skin damage is reduced.
Experimental studies have been reported which suggest that the trace element selenium may prevent cancers in animals. Ip et al., 4 Cancer Research 31 (1981); Schrauzer, 5 Bioinorganic Chemistry 275 (1976); Jansson et al., 91 Adv. Exc. Med. Biol. 305 (1977). In addition, state by state studies of mortality rates in the United States and various foreign countries show an inverse correlation between low soil selenium levels and human cancer mortality rates. Schrauzer et al., 7 Bioinorganic Chemistry 23 (1977); Shamberger et al., 2 Crit. Rev. Clin. Lab. Sci. 211 (1971).
Retrospective analyses have established that human patients with low plasma selenium levels are more likely to develop skin cancer than patients with high plasma selenium levels. Clark et al. 6 Nutrition and Cancer 13 (1984). These analyses took into account other important causes of skin cancer, such as excess exposure to sunlight, arsenic and ionizing radiation, but relied on the natural occurrence of selenium from the patients' diets. Subsequent prospective studies are currently in progress to evaluate the prophylactic efficacy of dietary selenium supplements, such as selenium enriched Brewer's yeast, in patients with marked sun exposure and a recent history of skin cancer, but results are not yet available.
Two studies have been conducted in mice, evaluating the effect of oral administration of sodium selenite on the carcinogenic potential of UV light in hairless mice. Thorling et al. 91 Acta Path. Microbiol. Immunol. Scand. Sect. A 81 (1983); Overrad et al. 27 Cancer Letters 163 (1985). Those studies showed that oral administration of sodium selenite rendered the mice more resistant to the acute and sub-acute effects of UV radiation, i.e inflammation and pigmentation, and also that oral administration of selenium mediated a dose-dependent selenium protection against UV-induced skin cancer. Unfortunately, the oral doses used in these studies resulted in a moderate inhibition of animal growth rate, as reflected in the decreased weight gain of the selenium-treated mice relative to the controls.
Selenium has been incorporated in topically applied shampoos or lotions for the treatment of seborrheic dermatitis and tinea versicoler. For this application, selenium sulfide is used at levels of 1.0-2.5%. Selenium sulfide applied topically does not penetrate the skin to give increased levels of selenium in the serum or liver.